High-throughput metagenomics analysis in early and precise diagnosis of eosinophilic meningoencephalitis complicated with respiratory failure: A case report

Rationale: Human infection with Angiostrongylus cantonensis is uncommon and has only been sporadically reported in the literature. Patients infected with A cantonensis usually have a delayed diagnosis and sometimes a poor prognosis. Patient concerns: A 70-year-old woman presented to the respiratory department with complaints of headache, chest pain, myalgia, fatigue, and anorexia for 7 days. Diagnoses: Complete blood count showed eosinophilia. The serum was tested showing a positive finding of A cantonensis antibody. Cerebrospinal fluid was tested using high-throughput metagenomics analysis and 16 reads for A cantonensis were mapped. The patient was diagnosed with A cantonensis infection. Interventions: The patient received a 7-day course of albendazole and 4-day course of prednisone. Outcomes: When discharged from the hospital, the patient still suffered from fatigue and poor memory. Aminotransferase levels were high due to albendazole’s liver toxicity. In a post-discharge follow-up about 1 month later she had recovered completely both physically and mentally, and peripheral eosinophil count and aminotransferase levels were both normal. Lessons: Because the direct identification of parasites is difficult, high-throughput metagenomics analysis may provide a reliable alternative tool for the diagnoses of infection with A cantonensis. When albendazole is prescribed, caution must be taken with respect to its liver toxicity.


Introduction
Angiostrongyliasis cantonensis was first discovered in the pulmonary arteries and hearts of domestic rats in Guangzhou (Canton), China, by Chen in 1935. [1] A cantonensis occasionally causes human angiostrongyliasis manifesting as eosinophilic meningitis or meningoencephalitis. [2] In recent years, with the popularization of high-throughput metagenomics analysis to diagnose diseases of unknown origin or cause, A cantonensis was detected in several cases, as A cantonensis sequences were found positive in samples from patients. [3][4][5] Here, we describe a case of human A cantonensis with a typical manifestation of eosinophilic meningoencephalitis with the help of high-throughput metagenomics analysis.
A 70-year-old woman patient presented to the respiratory department with compliant headache, chest pain, myalgia, fatigue, and anorexia for 7 days and was admitted to the hospital the next day. In her medical history, a surgery was performed for right nephroureterolithiasis 35 days ago in the same hospital.
Written fully informed consent has been given for all treatment and tests and recorded from the patient's son. Identifiable information has been excluded from the manuscript and written informed consent was obtained from the patient's son to publish the medical record and clinical data involved in this case report.
The authors have no funding and conflicts of interest to disclose.
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
The whole work was in accordance with the Declaration of Helsinki. As this is a case report without experimental intervention during routine care, formal approval of research ethics is not required.
The vital signs were stable but she had response lag and tenderness when palpated on the head, chest and back. The complete blood count showed an elevated eosinophil count of up to 2.42 × 10 9 /L, accounting for 31% of whole blood white blood cells. The total IgE was 1723 IU/mL (reference range: 1-100 IU/mL) and IgG 20.2 g/L (reference range: 7-16 g/L). The neutrophil count was in the normal range with respect to both the absolute count and the differential percentage. Arterial blood gas analysis revealed hypoxemia with PaO2 58.8 mm Hg and the PaO 2 /FiO 2 ratio 280 mm Hg. The chest computed tomography (CT) scan showed mild bilateral hydrothorax and the brain CT showed scattered ischemic foci. The D dimer was 4.07 μg/ mL (reference range: 0-0.5 μg/mL) and there was pulmonary embolism in the distal pulmonary arterial branches bilaterally by CT angiography (Fig. 1).
After admission to investigate the causes of peripheral eosinophilia, a series of parasite antibodies were tested resulting in a positive finding of the A cantonensis antibody in the serum of the patient. None of other common parasite antibody was positive.
Interestingly a review of her past medical history when she received the right nephro-ureterolithiasis surgery about one month ago showed a completely normal eosinophil count and percentage in the complete blood count. Her son provided an additional detail that when discharged from the hospital the patient and her family members got together to have a meal in nearby restaurant and a dish of oncomelania snails was consumed and the patient ate "only one" snail.
A cantonensis infection was suspected and then a lumbar puncture was arranged. Cerebrospinal fluid (CSF) was clear in color, but pressure was slightly elevated to 205 mm H 2 O. The pandy test was positive. The total cell count was 327 × 10 6 /L and the differential cytological count showed that eosinophils accounted for 63%. The chlorite concentration was 118.5 mmol/L (reference range: 120-132 mmol/L). The glucose concentration was 2.15 mmol/L. The protein concentration was 919 mg/L (reference range: 120-600 mg/L). No parasite was found with neither naked eyes nor under a microscope.
The A cantonensis antibody in CSF was negative. CSF was tested with high-throughput metagenomics analysis and 16 reads for A cantonensis were mapped (Fig. 2). None of the reads of virus, bacteria, fungus, or other parasites were mapped in the CSF.
The final diagnosis was A cantonensis. The differential diagnosis included other parasitic infections of the brain that may have manifestation of peripheral and central eosinophilia, but there was on other supportive microbial evidence. Albendazole 200 mg twice a day and prednisone 30 mg once a day orally were prescribed. Albendazole, an antiparasitic agent, and prednisone were chosen to prevent anaphylaxis according to the Chinese guidelines for the diagnosis and treatment of infection with angiostrongyliasis cantonensis.
The patient had a significant improvement in symptoms including neurologic status, myalgia, and appetite the next day. On the sixth day of treatment, the eosinophil count returned to 1.27 × 10 9 /L and the percentage was 17.8% and on the eighth day the eosinophil count was 0.73 × 10 9 /L and the percentage was 13.4%. On day 6 of treatment, alanine transaminase, gamma-glutamyl transferase and aspartate aminotransferase increased to 84 U/L (normal range: 7-40 U/L), 64 U/L (normal range: 13-35 U/L) and 61 U/L (7-45 U/L), respectively. The liver toxicity of albendazole was reported in the literature and usually recovered after discontinuation of albendazole administration. [6][7][8] The patient received a 7 day course of albendazole and a 4 day course of prednisone. When discharged from the hospital, she still suffered from fatigue, unable to stand up, and bad memory. In a post-discharge follow-up about a month later she had recovered completely both physically and mentally, and peripheral eosinophil count and aminotransferase were both normal (Fig. 3).

Discussion
A cantonensis is widely spread from its traditional endemic regions of the Pacific islands and Southeast Asia to the American continent, including the USA, Caribbean islands, and Brazil. [9] Shen Zhen City, the place where this patient lived, about 100 km away from Canton City, is located in a subtropical area that is a favorable habitat for the A cantonensis host, such as oncomelania snails. Inhabitants can be exposed to A cantonensis by eating intermediate or paratenic hosts, or vegetables contaminated by larvae. [10] This patient had a clear history of exposure as she consumed the oncomelania snail one month ago. This exposure was believed to be causal, as the eosinophil count in the complete blood count one month ago right after surgery was normal. Human susceptibility to A cantonensis may vary from person to person, as other family members who ate together kept healthy.
Most human angiostrongyliasis manifests itself as eosinophilic meningitis or meningoencephalitis, the clinical features are quite obvious with respect to peripheral blood and CSF eosinophilia, neurolgical disorders including headache, myalgia, and some nonspecific symptoms such as nausea and fainting. [2,4,9,10]   However, a timely diagnosis is not easy to achieve in clinical practice. Delayed diagnosis is quite common, as many patients were not correctly diagnosed until 2 or 3 weeks after hospitalization. The low detection rate is one reason for delayed or even missed diagnosis; In one early literature reported in 1988 in Chinese, the positive detection of A cantonensis was less than 2%. A review of several recent case reports of human A cantonensis showed that few of these cases reported a positive finding of A cantonensis directly. [4,[10][11][12][13] Angiostrongyliasis is usually considered based on a history of mollusk consumption, clinical characteristics, eosinophilic pleocytosis in the CSF, and the identification of a positive antibody. [14] Infection with A cantonensis in humans is only reported sporadically in the literature. It may not be a common disease that physicians can often encounter, which is a barrier for them to make an early and timely diagnosis. Some patients died from the delayed diagnosis of A cantonensis infections at a young age who otherwise had a good prognosis if the patient received adequate treatment. [5,11] Peripheral eosinophilia is not specific for A cantonensis; however, the eosinophil count test is a component part of the whole blood cell test which is an essential test in the inpatient department, in such circumstances eosinophilia provides an important clue for the diagnosis of a parasite infection that includes A cantonensis infection.
This case was diagnosed early and treated quickly. Peripheral eosinophilia provided a vital clue. Eosinophilia can be considered part of drug allergy, as many patients with A cantonensis would have received various drugs when the therapeutic efficacy was unsatisfactory, [10] but eosinophilia is almost unexceptionally present in all patients infected with A cantonensis at the beginning of the disease.
The A cantonensis antibody test is reliable for diagnosis, providing a support for its specificity. However, a false negative result of the A cantonensis antibody would delay diagnosis in a timely manner. [5] The high-throughput metagenomics analysis has high sensitivity and specificity for the detection of microorganisms, which has become increasingly popular in recent years. A prospective study reported that the sensitivity of high-throughput metagenomics analysis in the identification of bacteria, fungi, virus and tuberculosis in CSF was 73.3, 80, 76 and 66.7%, respectively, while the specificity of high-throughput metagenomics analysis in the diagnosis of bacteria, fungi and tuberculosis in CSF was 95.9, 79.3 and 96.4%, respectively. [5,15] High-throughput metagenomics analysis is almost a complete representation of the organisms present in a host organism. A positive finding of pathogens from samples from body parts that are otherwise pathogen-free is especially reliable. Sometimes it is a final straw when doctors have a suspicion that a sort of unknown organism might be the etiologic factor but microorganism culture or other routine microbiologic tests fail to detect a pathogen. High-throughput metagenomics analysis can serve as a target-free identification in the diagnosis of rare central nervous system angiostrongyliasis, [5] it can also solidify the diagnosis of A cantonensis when traditional examinations are not adequate to make a definitive diagnosis, since high-throughput metagenomics analysis provides direct evidence for the presence of A cantonensis nucleic acids.